1. Field of the Invention
The present invention relates to a mobile satellite communication antenna suitable for a satellite communication and for receiving a satellite broadcasting by a mobile like a car and the like.
2. Description of Related Art
A conventional mobile satellite communication antenna, as shown in FIG. 4 to FIG. 6, comprises a flat main plate 51 and an auxiliary plate 52, and the main plate 51 and the auxiliary plate 52 overlap one another and are combined with screws 3.
The plate 51 is provided with a motor 55 provided with a gear 54 and a converter 57 having a probe 56.
Further, as shown in FIG. 6, a shaft 58 fixed to the auxiliary plate 52 is rotatably mounted with a pulley 59 having a groove 59a and a plurality of pulleys 59 having the constitution like this are arranged concentrically with respect to the center part of the main plate 51.
Further, a ring-shaped rotary member 60 comprising a formed product made of synthetic resin has a trapezoidal groove 60a having a gear part (not shown) on the whole outer periphery thereof, a ring-shaped protruding part 60b made on the lower part of the groove 60a, and a hole 60c made in the center part thereof.
Further, although not shown here, a plurality of antenna elements are formed concentrically on a disc-shaped antenna board 61, and the antenna board 61 is arranged on the top surface of the rotary member 60 in such a way that it closes the hole 60c and is fixed to the rotary member 60 with screws 62.
Further, a ring-shaped preventing member 63 made of a metal plate is arranged on the top surface of the rotary member 60 such that it is positioned outside the antenna board 61, and is fixed to the rotary member 60 with screws 64. When the preventing member 63 is fixed, a part of the preventing member 63 protrudes outward in the radial direction from the outer periphery of the rotary member 60.
An antenna board member 65 is composed of the rotary member 60, the antenna board 11 and the preventing member 63 and is rotatably supported by the pulley 59 with the ring-shaped protruding part 60b of the rotary member 60 retained by the grooves 59a of the plurality of pulleys 59.
In this respect, the center part of the antenna board 61 is in the state opposite to the probe 56 and supplies radio waves from the antenna elements to the probe 56.
Further, a toothed endless belt 66 is looped around the groove 60a having a gear part of the rotary member 60 and the gear mounted on the motor 55, and the antenna board member 65 is rotated by the motor 55 via the belt 66.
In this connection, the top end of the belt 66 looped around the groove 60a of the rotary member 60 is prevented from coming off by the preventing member 63 protruding outward in the radial direction from the rotary member 60.
Further, a lever 68 is mounted on the plate 52 such that it can be turned around a shaft 67, and a pulley 69 is rotatably mounted on the lever 68. A spring 70 is interposed between the lever 68 and the plate 52.
The pulley 69 is brought into contact with the outer side of the belt 66 and is pulled by the spring 70 via the lever 68 to eliminate the looseness of the belt 66.
The mobile satellite communication antenna having the constitution described above is mounted on the roof of a mobile like a car and the like, and the antenna board member 65 is rotated by the motor 55 with the movement of the mobile to adjust the orientation to a geostationary satellite.
In the conventional mobile satellite communication antenna, since the antenna board 61 and the preventing member 63 for preventing the belt 66 from coming off are attached to the rotary member 60, the number of parts are increased and the costs increases. Further, a space in which the preventing member 63 is mounted is needed, whereby the size becomes large.
Further, since the rotary member 60 is made of synthetic resin, the expansion and shrinkage of the rotary member 60 caused by a change in environmental temperature outdoors is extremely large, which produces another problem that the antenna board member 65 can not be smoothly rotated and is finally put out of rotation.